The present invention relates to the treatment of polypyrrolidone fibers with a certain chemical to reduce fibrillation.
Preparation of polypyrrolidone fibers is known in the art, see for example Barnes U.S. Pat. No. 3,721,652.
Polypyrrolidone fibers have a number of advantages, but one disadvantage they suffer from is fibrillation, that is, the fibers as such and the fibers when in the form of yarns and fabrics develope small fibrils when subjected to washing. These fibrils are hair-like whiskers still attached to the main fiber at one end.
Fibrillation is a phenomenon induced in fibrous materials by the application of stress, and is characterized by the development of hair-like shoots to the parent filament or fiber of longitudinal sections of material which are usually referred to as "fibrils". The dimensions of the fibrils are small compared to those of the original filament fiber. The formation of the small attached fibrils is referred to as fiber breakdown or fibrillation and can readily be observed under the microscope, where the presence of fibrils on the main fiber strand may be seen. In undyed fabrics the presence of fibrils may not be apparent to casual inspection but it is evidenced by dulling of the finish, change in hand, and can be seen on microscopic examination. Dyed fibers of melt extruded and oriented polypyrrolidone readily display the effects of fibrillation which causes a loss of color intensity. Both the change in hand and the loss of color intensity are undesirable in commercial articles.
The effects of fibrillation become evident on repeated laundering and tumble-drying and substantial absence of fibrillation is thus necessary for good launderability of a fabric.
U.S. Pat. No. 3,318,658 is concerned with improving the resistance of polypyrrolidone fibers to fibrillation. According to U.S. Pat. No. 3,318,658, polypyrrolidone fibers are subjected to the action of formaldehyde in the presence of an acidic methylolation catalyst under nonsolubilizing conditions, and then water is removed to effect cross-linking.
U.S. Pat. No. 3,318,658 states in column 3, line 59, that the term "formaldehyde" is used therein
" . . . to encompass aldehydic agents such as formaldehyde and sources thereof, e.g., paraformaldehyde, to methylol urea, dimethylol ethylene urea, dimethyl formal, saligenin, formalin, hexamethylene tetramine, and the like."
With respect to the methylolation catalyst, the '658 patent states that methylolation catalysts which are useful for the process
" . . . are those reagents or combination of reagents which produce aqueous solutions of pH values ranging from pH 1 to pH 5. Specific examples of such agents include dilute aqueous solutions of strong acids, water-soluble weak acids and salts of acids with weaker bases. Such substances include 0.01 N aqueous hydrochloric acid, ammonium chloride, zinc chloride, sodium bisulfite, ammonium sulfate, oxalic acid and very dilute formic acid. Glycolic and lactic acid are also suitable as catalysts but have the disadvantage of plasticizing the fibers and thus degrading their mechanical properties."
One disadvantage of using formaldehyde or formaldehydeforming materials for reduction of polypyrrolidone fiber fibrillation is that a formaldehyde odor frequently remains after curing the treated fibers or fabrics.
The present invention is particularly concerned with the use of dimethyloldihydroxyethyleneurea, which has also been used to give cotton fabrics a permanent-press characteristic.